Basics Of Object Oriented Programming ( OOP )

Object Oriented Programming 

• It treats data as a critical element in program development and does not allow it to flow freely around the system.
• It ties data more closely to the functions that operate on it and protects it from accidental modification from outside functions.
• OOP allows decomposition of a problem into a number of entities called objects and then builds data and functions around these objects.
• The data of an object can be accessed only by the functions associated with that object.
• Functions of one object can access the functions of another object.

Organization of data and function in OOP

Characteristics of OOP

• Emphasis is on data rather than procedure.
• Programs are divided into objects.
• Data Structures are designed such that they characterize the objects.
• Functions that operate on data of an object are tied together in the data structure.
• Data is hidden and can not be accessed by external functions.
• Objects may communicate with each other through functions.
• New data and functions can be added easily whenever necessary.
• Follows bottom-up approach in program design.

Basic concepts of OOP

1.Classes

• Classes are user-defined data types
• A class is a collection of Data member and member functions.
• Variables declared in a class are called data members and functions declared in class are called member functions or methods.
• Objects are variables of type class. Once a class has been defined, we can create any number of objects belonging to that class.
• Each object is associated with the data of type class with which they are created.
• If Fruit is a class, then apple, orange, banana etc. are the objects of the class Fruit.
• Class is a logical structure.

2.Object

• Basic run-time entities in an object-oriented system i.e. fundamental building blocks for designing a software.
• It is a collection of data members and associated member functions(method).
• An object represents a particular instance of a class.
• An object has 3 characteristics:

1. Name
2. State
3. Behavior

• Objects take up space in the memory and have associated addresses.
• When a program is executed, objects interact by sending messages to one another.
• Example : Book, Bank, Customer, Account etc.

3.Data Abstraction

• Abstraction refers to the act of representing essential features without including the background details or explanation.
• Data abstraction is an encapsulation of object’s state and behavior.
• Data abstraction increases the power of programming languages by creating user-defined data types.
• Classes use the concept of abstraction and are defined as a list of abstract attributes(data members) and functions(methods).
• Since classes use the concept of data abstraction, they are also used as Abstract Data Type(ADT).

4.Encapsulation

• Data encapsulation combines data and functions into a single unit
• called class.
• When using data encapsulation, data is not accessed directly, it is only accessible through the methods present inside the class.
• Data encapsulation enables data hiding, which is an important concept of OOP.
• Example : Capsules are wrapped with different medicines.

5.Inheritance

• It is the process by which one object can acquire the properties of another.
• It allows the declaration and implementation of new class/classes from existing classes.
• The existing class is known as base class/parent class/super class and the new class/classes is/are known as derived class/child class/sub class.
• It uses the concept of Reusability.

Types of Inheritance :

1. Single Inheritance
2. Multiple Inheritance
3. Multilevel Inheritance
4. Hierarchical Inheritance
5. Hybrid Inheritance

6.Polymorphism

• The ability to take more than one form is known as Polymorphism.
• An operation may exhibit different behaviors in different instances. The behavior depends upon the types of data used in the operation.
• + operator can be used to add 2 numbers and the result is the sum of two numbers.
• Same + operators can be used to add 2 strings and the result is concatenation of 2 strings.
• This process of making an operator to exhibit different behaviors in different instances is known as operator overloading.

Polymorphism (Function Overloading)

• A single function name can be used to handle different numbers and different types of arguments.
• Using a single function name to perform different types of tasks is known as function overloading.

7.Message Passing

• Any processing is accomplished by sending messages to objects.
• A message for an object is a request for execution of a procedure/function.
• It invokes a function on the receiving object that generates the desired result.
• Message passing involves specifying the name of the object, name of the function(message) and information to be sent.